In conventional liquid crystal displays (LCDs), plasma displays panels (PDPs), and the like, a variety of sputtering apparatuses are proposed for sequentially depositing thin films such as transparent electrodes, dielectric films, insulating films, and the like with a uniform thickness on large-area glass substrates in large quantities. One of these apparatuses is an inline sputtering apparatus. In this apparatus, a plurality of sputtering cathodes are arranged in a line within its sputter deposition chamber.
While carriers (transfer devices) on which substrates are held are moved at a constant speed along the orientation direction of the sputtering cathodes, a target material ejected from the target is deposited on the substrates, to thereby form a desired thin film on the substrates. The apparatus is capable of sequentially depositing a thin film with a uniform thickness on large-area glass substrates in large quantities (Patent Document 1).
In the inline sputtering apparatus, it is required to simultaneously perform heating, sputtering, transfer of the carriers, and the like from the time of the activation (start) of the apparatus to the production, in order to fulfill the following objects (1) to (4).
(1) To stabilize the temperature distribution among the structures around the carriers and the target.
(2) To stabilize the degassing from the structures around the carriers and the target.
(3) To remove impurities attached to the surface of the target. This is generally referred to as pre-sputtering.
(4) To increase the discharge electric power of the target in a stepwise manner. This is generally referred to as ramp-up.
At the activation of such apparatuses, instead of a substrate used for a product, a glass plate with the same shape is used as a dummy substrate.
Furthermore, in manufacturing products different in specifications, it is required to modify the deposition conditions, the sputtering, the carrier transfer, and the like. Also in this case, instead of a substrate used for a product, a glass plate with the same shape is used as a dummy substrate.
Moreover, when maintenance of the apparatus is performed, problems can occur, or other times, it is required to cool the heated portion inside the apparatus approximately to room temperature, and then to open the vacuum region of the apparatus to air. The reason is that if the vacuum region is opened to air at temperatures not less than 100° C., the surface of the heated portion in the vacuum region is oxidized, making the environment in the subsequent sputtering unstable.
Thus, the activation or deactivation (stop) of the apparatus takes a considerable time. Therefore, for example, if a delay in delivery of substrates for products has caused a disruption of supply of substrates to the apparatus during normal production operation, the deposition conditions, the sputtering, the carrier transfer, and the like are often retained in order to nullify the time required for stopping and reactivating the apparatus for swift resumption of the production.
In such retention of the apparatus, instead of a substrate used for a product, a glass plate with the same shape is used as a dummy substrate. Recent years have seen proposals of dummy substrates using a metal plate made of a nickel-based alloy such as Inconel, a nickel-plated material, aluminum, or the like instead of a glass substrate (Patent Documents 2 and 3).
Patent Document 1: Japanese Unexamined Patent Publication, First Publication No. 2002-60938
Patent Document 2: Japanese Unexamined Patent Publication, First Publication No. 2003-229369
Patent Document 3: Japanese Unexamined Patent Publication, First Publication No. H11-152564
Here, conventional inline sputtering apparatuses have the following problems because they use a glass substrate as a dummy substrate at the time of the activation and the deactivation of the apparatus, or at the time of the retention/modification of deposition conditions:
(1) In the case of the activation of the apparatus and the retention/modification of deposition conditions, the stress of the deposition increases as the amount of deposition on the glass substrate increases. As a result, this makes the load on the glass substrate higher, leading to a problem in that glass cracking and the like may occur at the time of the deposition, the carrier transfer, and the attachment/detachment to/from the carrier. In the case where a glass substrate is used as a dummy substrate, the number of times it is used is normally limited to approximately six or seven, although the number of uses slightly varies according to apparatuses and the like.
(2) The activation and deactivation of the apparatus each takes several hours. An occurrence of problems such as glass cracking results in a long stop time of the apparatus, leading to not only a problem of reduction in productivity, but also a problem in that a delay in delivery of products may be caused.
Especially in a production line operated for 24 consecutive hours or the like, the number of times a single dummy substrate is used is reduced to prevent a problem such as glass cracking. Therefore, a multitude of dummy substrates are required.
In recent years, due to the upsizing of a glass substrate resulting from the upsizing of the panel size of the liquid crystal displays (LCDs) and the plasma display panels (PDPs), dummy substrates have been upsized. Therefore, a problem such as glass cracking is also a cause of an increase in the cost of the dummy substrate.
Furthermore, in a conventional dummy substrate for which a metal plate is used, a heavier load is imposed on the carrier because metal has a specific gravity larger than that of a glass plate, although the metal plate is free from a problem such as glass cracking. To address this, if a metal plate with the same weight as that of the glass plate is to be used, it is required to make the metal plate very thin, leading to a new problem of insufficient strength and the like.